Re: [PATCH] xen/x86: prevent addition of .note.gnu.property if livepatch is enabled

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Thu, Nov 07, 2024 at 04:14:20PM +0100, Jan Beulich wrote:
> On 07.11.2024 15:59, Roger Pau Monne wrote:
> > GNU assembly that supports such feature will unconditionally add a
> > .note.gnu.property section to object files.  The content of that section can
> > change depending on the generated instructions.  The current logic in
> > livepatch-build-tools doesn't know how to deal with such section changing
> > as a result of applying a patch and rebuilding.
> > 
> > Since .note.gnu.property is not consumed by the Xen build, suppress its
> > addition when livepatch support is enabled.
> > 
> > Signed-off-by: Roger Pau Monné <roger.pau@xxxxxxxxxx>
> 
> Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>

Thanks.

> Just one thing though:
> 
> > --- a/xen/arch/x86/arch.mk
> > +++ b/xen/arch/x86/arch.mk
> > @@ -26,6 +26,12 @@ $(call as-option-add,CFLAGS,CC,"invpcid 
> > (%rax)$(comma)%rax",-DHAVE_AS_INVPCID)
> >  $(call as-option-add,CFLAGS,CC,"movdiri 
> > %rax$(comma)(%rax)",-DHAVE_AS_MOVDIR)
> >  $(call as-option-add,CFLAGS,CC,"enqcmd 
> > (%rax)$(comma)%rax",-DHAVE_AS_ENQCMD)
> >  
> > +# Disable the addition of a .note.gnu.property section to object files when
> > +# livepatch support is enabled.  The contents of that section can change
> > +# depending on the instructions used, and livepatch-build-tools doesn't 
> > know
> > +# how to deal with such changes.
> > +$(call 
> > cc-option-add,CFLAGS-$(CONFIG_LIVEPATCH),CC,-Wa$$(comma)-mx86-used-note=no)
> > +
> >  # Check to see whether the assmbler supports the .nop directive.
> >  $(call as-option-add,CFLAGS,CC,\
> >      ".L1: .L2: .nops (.L2 - .L1)$(comma)9",-DHAVE_AS_NOPS_DIRECTIVE)
> 
> I don't really like this being squashed between two as-option-add invocations.
> Can this be moved down, e.g. before or after the XEN_IBT chunk? Happy to move
> while committing ...

Feel free to move it.

Roger.